Monolithic high refractive index photonic devices

ABSTRACT

Fabricating a high refractive index photonic device includes disposing a polymerizable composition on a first surface of a first substrate and contacting the polymerizable composition with a first surface of a second substrate, thereby spreading the polymerizable composition on the first surface of the first substrate. The polymerizable composition is cured to yield a polymeric structure having a first surface in contact with the first surface of the first substrate, a second surface opposite the first surface of the polymeric structure and in contact with the first surface of the second substrate, and a selected residual layer thickness between the first surface of the polymeric structure and the second surface of the polymeric structure in the range of 10 μm to 1 cm. The polymeric structure is separated from the first substrate and the second substrate to yield a monolithic photonic device having a refractive index of at least 1.6.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 15/684,530entitled “MONOLITHIC HIGH REFRACTIVE INDEX PHOTONIC DEVICES” filed onAug. 23, 2017, which claims the benefit of U.S. Application No.62/380,093 entitled “MONOLITHIC HIGH REFRACTIVE INDEX PHOTONIC DEVICES”filed on Aug. 26, 2016, and U.S.

Application No. 62/502,973 entitled “MONOLITHIC HIGH REFRACTIVE INDEXPHOTONIC DEVICES” and filed on May 8, 2017, all of which areincorporated herein by reference in their entirety.

TECHNICAL FIELD

This invention generally relates to monolithic high refractive indexphotonic devices.

BACKGROUND

Fabrication of photonic devices is typically a multi-step process thatincludes patterning of a substrate with nano- and microstructures.Patterning may be achieved by a lithographic technique such as UVlithography, nanoimprinting, or the like. In some cases, a pattern istransferred into a thin film or substrate by etching (e.g., plasmaetching or liquid etching). Thus, fabrication of photonic devices isusually expensive and slow, involving multiple processing steps.

SUMMARY

In a first general aspect, fabricating a high refractive index photonicdevice includes disposing a polymerizable composition on a first surfaceof a first substrate and contacting the polymerizable composition with afirst surface of a second substrate, thereby spreading the polymerizablecomposition on the first surface of the first substrate (e.g., betweenthe first surface of the first substrate and the first surface of thesecond substrate). The polymerizable composition is cured to yield apolymeric structure having a first surface in contact with the firstsurface of the first substrate, a second surface opposite the firstsurface of the polymeric structure and in contact with the first surfaceof the second substrate, and a selected residual layer thickness betweenthe first surface of the polymeric structure and the second surface ofthe polymeric structure in the range of 10 μm to 1 cm. The polymericstructure is separated from the first substrate and the second substrateto yield a monolithic photonic device having a refractive index of atleast 1.5 or at least 1.6.

Implementations of the first general aspect may include one or more ofthe following features.

At least one of the first substrate and the second substrate may be apatterned mold, the first surface of the patterned mold definingprotrusions and recessions. Some implementations of the first generalaspect include coating the first surface of the first substrate, thefirst surface of the second substrate, or both with a release layerbefore disposing the polymerizable composition on the first surface ofthe first substrate. In one example, the first surface of the secondsubstrate is coated with a release layer before the polymerizablecomposition is contacted with the first surface of the second substrate.

Some implementations of the first general aspect include heating thefirst substrate to at least 100° C. before disposing the polymerizablecomposition on the first surface of the first substrate. The firstgeneral aspect may also include heating the first substrate, the secondsubstrate, or both to at least 100° C. before contacting thepolymerizable composition with the first surface of the secondsubstrate.

Some implementations of the first general aspect include partiallypolymerizing the polymerizable composition before disposing thepolymerizable composition on the first surface of the first substrate.Contacting the polymerizable composition with the second substrate mayinclude forming an acute angle between the first substrate and thesecond substrate, and reducing the value of the acute angle until thefirst substrate and the second substrate are parallel.

Curing the polymerizable composition may include heating thepolymerizable composition to a temperature less than 100° C. or between100° C. and 350° C. Curing the polymerizable composition may includecuring the polymerizable composition for a duration of less than 5minutes.

In some cases, curing the polymerizable composition includes irradiatingthe polymerizable composition with ultraviolet (UV) radiation. Aduration of the UV radiation may be less than 5 minutes. An intensity ofthe UV radiation may be substantially constant throughout the durationof the irradiation of the polymerizable composition. In some cases, anintensity of the UV radiation is in a range from less than 30 mW/cm² toover 110 mW/cm², or greater than 50 mW/cm². In certain cases, anintensity of the UV radiation is in a range of 5 mW/cm² to 300 mW/cm².Irradiating the polymerizable composition with the UV radiation mayinclude irradiating a surface area of the polymerizable composition in arange of 1 cm² to 1000 cm². An intensity of the ultraviolet radiationmay be substantially constant over the irradiated surface area of thepolymerizable composition. In some cases, an intensity of the UVradiation is varied over the irradiated surface area of thepolymerizable composition to achieve a pre-defined local shrinkage inthe monolithic photonic device. The UV radiation may include at leastone of UVA, UVB, and UVC. In some cases, a wavelength of the UVradiation is in a range of 250 nm to 380 nm. In certain cases, awavelength of the UV radiation is in a range of about 315 nm to about400 nm (e.g., 365 nm±20 nm). In some cases, a wavelength of the UVradiation includes at least one of 365 nm, 380 nm, and 405 nm.

In certain cases, curing the polymerizable composition includes heatingthe polymerizable composition to a temperature between 100° C. and 350°C. and irradiating the polymerizable composition with UV radiation.

In some implementations, the selected residual layer thickness betweenthe first surface of the polymeric structure and the second surface ofthe polymeric structure is in a range of 250 μm to 500 μm. In somecases, the refractive index of the monolithic photonic device is atleast 1.65 or at least 1.7. The transmittance of the monolithic photonicdevice between 400 nm and 800 nm may be greater than 80%.

The polymerizable composition may include first monomers and secondmonomers, each first monomer having at least two vinyl, allyl, oracrylate moieties, and each second monomer having at least two thiolmoieties. In some cases, the polymerizable composition includes aphotoinitiator, a thermal initiator, or both. In certain cases, thepolymerizable composition includes a metal oxide. The metal oxide mayinclude at least one of titanium oxide, zirconium oxide, and zinc oxide.

In some implementations, the polymerizable composition includes 20 wt %to 90 wt % of a high viscosity multifunctional component, 5 wt % to 40wt % of a low viscosity mono- or multifunctional component, 0.2 wt % to5 wt % of a photoinitiator, 0.2 wt % to 2 wt % of a light stabilizer,and 0.2 wt % to 2 wt % of an antioxidant, and curing the polymerizablecomposition includes polymer crosslinking through a singlefunctionality. The polymerizable composition may include a surfactant.In some cases, the polymerizable composition includes inorganicnanoparticles or molecular level clusters.

In some implementations, the polymerizable composition includes 20 wt %to 80 wt % of a multifunctional component with a first reactive moiety,20 wt % to 80 wt % of a multifunctional component with a second reactivemoiety, 0.2 wt % to 5 wt % of a photoinitiator, 0.2 wt % to 2 wt % of alight stabilizer, and 0.2 wt % to 2 wt % of an antioxidant, and thefirst reactive moiety and the second reactive moiety are different, andcuring the polymerizable composition comprises polymer crosslinkingthrough cross-reaction through at least the first reactive moiety andthe second reactive moiety. In some cases, the polymerizable compositionincludes a surfactant. In certain cases, the polymerizable compositionincludes inorganic nanoparticles having a maximum particle size of 20nm.

The first substrate and the second substrate may be discs having athickness in a range of 300 μm to 10 mm. A total thickness variation ofthe first substrate and the second substrate is typically in a range of100 nm to 20 μm.

The photonic device may be optically transparent. In some cases, thephotonic device is a lens. In certain cases, a first surface of thephotonic device, a second surface of the photonic device, or both have apatterned surface defining protrusions and recessions, and a dimensionof each protrusion and recession is less than 10 nm, less than 100 nm,less than 1 μm, less than 10 less than 100 μm, or less than 1 mm.

In a second general aspect, a photonic device includes a monolithicstructure of a cured polymeric material having at least one patternedsurface defining protrusions and recessions. The refractive index of themonolithic structure is typically at least 1.6, and a minimum thicknessof the monolithic structure is typically in a range of 10 μm to 1 cm.

Implementations of the second general aspect may include one or more ofthe following features.

At least one of a first surface of the photonic device and a secondsurface of the photonic device opposite the first surface is a patternedsurface defining protrusions and recessions, and a dimension of eachprotrusion and recession is less than 10 nm, less than 100 nm, less than1 μm, less than 10 less than 100 μm, or less than 1 mm.

In some cases, the cured polymeric material includes a thiol-ene basedpolymer. In certain cases, the cured polymeric material includes a metaloxide. In one example, the cured polymeric material includes 0.1 wt % to30 wt % of the metal oxide. The metal oxide may include titaniumdioxide, zirconium dioxide, zinc oxide, or a combination thereof.

The refractive index of the monolithic photonic device is typically in arange of 1.6-1.9. The field of view of the photonic device (4:3 aspectratio) may be up to 50° or up to 70°. In some cases, the photonic deviceis optically transparent. In certain cases, the photonic device is alens.

Methods and materials are described herein for use in the presentapplication; other, suitable methods and materials known in the art canalso be used. The materials, methods, and examples are illustrative onlyand not intended to be limiting. All publications, patent applications,patents, and other references mentioned herein are incorporated byreference in their entirety. In case of conflict, the presentspecification, including definitions, will control.

Other features and advantages of the present application will beapparent from the following detailed description and figures, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a first exemplary process for fabrication of aphotonic device.

FIGS. 2A-2C depict oxo metal clusters.

FIG. 3 is a flowchart of a second exemplary process for fabrication of aphotonic device.

FIG. 4 depicts fabrication of an exemplary photonic device.

FIGS. 5A-5C, 6A-6C, and 7A-7C depict contacting a polymerizablecomposition with a substrate to reduce defect formation in a photonicdevice.

FIGS. 8A and 8B depict exemplary monolithic photonic devices.

FIGS. 9A-9D depict exemplary casting plates.

FIG. 10A is an image of a polymeric film irradiated with non-uniform UVintensity. FIG. 10B depicts irradiation of a polymeric composition witha non-uniform UV intensity.

FIG. 11 is a graph showing transmittance of light through a polymericsubstrate.

DETAILED DESCRIPTION

FIG. 1 is a flowchart describing a first exemplary process 100 forfabrication of a monolithic, optically transparent, high refractiveindex photonic device from a thiol-ene based polymer resin. As usedherein, “photonic device” generally refers to a device for generating,detecting, or manipulating photons through emission, transmission,modulation, signal processing, switching, amplification, or detection.Examples of photonic devices include lenses and eyepieces. As usedherein, a “monolithic” photonic device generally refers to a photonicdevice formed in a molding process as a single piece from a singlepolymerizable composition. That is, a monolithic photonic device is aseamless structure molded from a single material. As used herein,“optically transparent” generally refers to the physical property ofallowing light to pass through a material without being scattered. Asused herein, “high refractive index” generally refers to a refractiveindex (n) greater than 1.6. In one example, “high refractive index”refers to n greater than 1.6 and less than 1.9. As used herein,“thiol-ene based polymer resins” generally refers to a polymerizablecomposition including “thiol” monomers having at least two thiolmoieties and “ene” monomers having at least two vinyl, allyl, oracrylate moieties. A thiol-ene based polymer resin may also include aphotoinitiator, a thermal initiator, an inorganic compound, astabilizer, or any combination thereof.

As used herein, total thickness variation (TTV) refers to the differencebetween the maximum and minimum values of the thickness of a substratein a series of point measurements across a dimension of a substrate. Fora substrate having a patterned surface, the TTV refers to anapproximation assessed by ignoring contributions of pattern features tothe thickness. By way of explanation, a thickness (or height) of atypical feature on a patterned substrate is about 10 nm to 150 nm. Thatthickness is primarily governed by the trench depth of the template,which can vary by 10% (e.g., 1 nm to 15 nm). The TTV of an unpatternedsubstrate typically exceeds 100 nm, and is sometimes on the order ofmicrons. Thus, the additional variation in thickness of a patternedsubstrate introduced by the pattern features is negligible, and can beignored as an approximation. Accordingly, the thickness of a patternedsubstrate assessed at a location that includes a protrusion may beapproximated by subtracting a given feature thickness from the assessedthickness to yield an “adjusted” thickness, while thickness of apatterned substrate assessed at a location without a protrusion isunchanged. That is, the adjusted (reduced) thickness of a feature areaand a native thickness of an unpatterned area will be used to calculateTTV for a substrate having a patterned surface. The low TTV valuesdescribed herein are understood to result at least in part from flatoptical grade glass templates, polished to meet a desired flatness, aswell as methods described herein to minimize or reduce uneven materialshrinkage during curing.

In 102, a polymerizable composition is disposed on a first surface of afirst substrate. The first substrate may be heated (e.g., in a range of100° C. to 250° C.) while the polymerizable composition is disposed onthe first surface of the first substrate. Disposing the polymerizablecomposition on the first substrate may include casting a single volumeof the polymerizable composition on the first substrate. The firstsubstrate is typically a disc or wafer with a thickness in a range of300 μm to 10 mm and a diameter in a range of 5 cm to 30 cm. The firstsubstrate may be formed of material including silicon, quartz, glass, orother solid substance having a glass transition temperature that exceeds250° C. The TTV of the first substrate is typically in a range of 100 nmto 20 μm. Optical performance of the resulting photonic device istypically enhanced by increasing the thickness and decreasing TTV of thefirst substrate. In one example, the first surface of the firstsubstrate is a flat surface. In another example, the first surface ofthe first substrate is a patterned surface, and the first substrate is apatterned mold. As used herein, “patterned surface” and “patterned mold”generally refer to protrusions and recessions having a dimension (e.g.,length, width, or height) less than 10 nm, less than 100 nm, less than 1μm, less than 10 less than 100 μm, or less than 1 mm. The patternedsurface or patterned mold typically includes nanostructures (e.g.,structures having all dimensions less than less than 1 μm or less than100 nm), microstructures (e.g., structures having all dimensions in arange of 1 μm to less than 1 mm, less than 100 μm, or less than 1 μm),or any combination thereof.

Before the polymerizable composition is disposed on the first surface ofthe first substrate, the first substrate may be coated with a releaselayer. A thickness of the release layer is typically in a range of 1 nmto 30 nm thick. A release layer may be a fluorosilane coating, a metalcoating, a metal oxide coating, or any other coating suitable for usewith a curable high index polymerizable composition. In one example, apolydimethylsiloxane (PDMS) release layer is formed on the firstsubstrate by a process that includes cleaning the first substrate,coating the first substrate with a thin layer of PDMS, and curing thePDMS by placing the first substrate on a hot plate and heating thesubstrate (e.g., at 200° C. for 15 min).

In some embodiments, high index polymerizable compositions includecomponents in the amounts listed in Tables 1 and 2. Table 1 listscomponents in a polymerizable composition in which crosslinking occursthrough a single type of functional group. Suitable functional groupsinclude acrylate and epoxy functional groups. Exemplary compoundsinclude 9,9-bis(4-hydroxyphenyl)fluorene diglycidyl ether,4,4-bis(glycidyloxy-ethylthio)diphenylsulfide, and phenylthioethylglycidyl ether. Table 2 lists components in a polymerizable compositionin which crosslinking occurs through a cross-reaction of two or moredifferent functional groups (e.g., a thiol and an ene).

TABLE 1 Polymerizable compositions in which crosslinking occurs througha single functional group High viscosity multifunctional component20~90% (w/w) Low viscosity mono- or multifunctional 5~40% (w/w)component Photoinitiator 0.2~5% (w/w) Light stabilizer 0.2~2% (w/w)Antioxidant 0.2~2% (w/w) Surface active agent 0~5% (w/w) Inorganicnanoparticle or molecular level 0~40% (w/w) cluster

TABLE 2 Polymerizable compositions in which crosslinking occurs throughcross-reaction of two or more different functional groupsMultifunctional component with 20~80% (w/w) functionality type 1Multifunctional component with 20~80% (w/w) functionality type 2Photoinitiator 0.2~5% (w/w) Light Stabilizer 0.2~2% (w/w) Antioxidant0.2~2% (w/w) Surface active agent 0~5% (w/w) Inorganic nanoparticle ormolecular 0~40% (w/w) level cluster

In certain embodiments, polymerizable compositions in which crosslinkingoccurs through cross-reaction of two or more different functional groupsinclude a mixture of ene monomers (each ene monomer having anycombination of at least two of vinyl, allyl, and acrylate moieties) andthiol monomers (each thiol monomer having at least two thiol moieties).The ene monomers and thiol monomers may be combined in a stoichiometricratio, with the number of available ene moieties equal to the number ofthiol moieties, or any molar ratio (e.g., less than or greater than thestoichiometric ratio) effective to yield a polymer composite in the formof a free-standing polymeric structure. A few examples of suitable enemonomers are shown below.

A few examples of thiol monomers include 1,2-ethanedithiol,1,5-pentanedithiol, and 1,3-benzenedithiol, shown below.

The polymerizable composition may be doped with one or more inorganiccomponents, such as TiO₂, ZrO₂, ZnO, and the like, in a concentration of0.1 wt % to 50 wt % (e.g., 0.1 wt % to 10 wt % or 10 wt % to 30 wt %, or10 wt % to 50 wt %).

In some cases, the polymerizable composition includes one or morepolymerization initiators (e.g., a photoinitiator, a thermal initiator,or both). The concentration of the polymerization initiator is typicallyin a range of 0.1 wt % to 10 wt % (e.g., 0.1 wt % to 2 wt % or 2 wt % to10 wt %). Examples of suitable photoinitiators include2-benzyl-2-(dimethylamino)-4′-morpholinobutyrophenone;4′-tert-butyl-2′,6′-dimethyl-acetophenone; 2,2-diethoxyacetophenone;2,2-dimethoxy-2-phenylacetophenone;diphenyl(2,4,6-trimethylbenzoyl)phosphineoxide/2-hydroxy-2-methylpropiophenone; 4′-ethoxyacetophenone;3′-hydroxyacetophenone; 4′-hydroxyacetophenone; 1-hydroxy-cyclohexylphenyl ketone; 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone;2-hydroxy-2-methylpropiophenone;2-methyl-4′-(methylthio)-2-morpholinopropiophenone;1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one, and4′-phenoxy-acetophenone. Examples of suitable thermal initiators includetert-amyl peroxybenzoate, 4,4-azobis(4-cyanovaleric acid),1,1-azobis(cyclohexanecarbonitrile), 2,2-azobisiso-butyronitrile (AIBN),benzoyl peroxide, 2,2-bis(tert-butylperoxy)butane,1,1-bis(tert-butylperoxy)cyclohexane, 5-bis(tert-butylperoxy)2,5-dimethyl-3-hexyne,1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, and2,4-pentanedione peroxide. Other compounds that generate reactivespecies through free radical formation may also be used aspolymerization initiators.

The polymerizable composition may include a stabilizer or inhibitor toincrease the shelf life of the composition. Suitable stabilizers includeacidic components, radical stabilizers, and monomers such as4-allyloxy-2-hydroxybenzophenone; 2-tert-butyl-4-ethylphenol;2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol;2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol;2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]ethyl methacrylate;2-(2H-benzotriazol-2-yl)-4-methyl-6-(2-propenyl)phenol;2-(4-benzoyl-3-hydroxyphenoxy)ethyl acrylate;5-chloro-2-hydroxybenzophenone;2,6-di-tert-butyl-4-(dimethylaminomethyl)phenol;2,4-dihydroxybenzophenone; 2,2′-ethylidene-bis(4,6-di-tert-butylphenol);and similar compounds.

The polymerizable composition may include an anti-oxidant to inhibit orprevent certain chemical reactions that result in degradation of thepolymer due to certain weather conditions. Suitable antioxidants includebenzofuranone, hindered phenols, and secondary aromatic amines.

The polymerizable composition may include a surface active agent. Thesurface active agent may have at least one functional group such as athiol or ene as well as at least one non-polar functional group such asalkyl, aryl, or fluoride. Suitable examples of surface active agentsinclude alkylthiols such as octanethiol or decanethiol.

A process for fabricating high refractive index materials includecombining first (ene) monomers, second (thiol) monomers, and optionallyone or more inorganic components and other additives (e.g.,polymerization initiators, stabilizers) to yield a composite mixture,and curing the composite mixture to yield a polymer composite. In somecases, polymerizable compositions described herein are formed by “click”reactions that result in covalent crosslinking of ene moieties (e.g.,vinyl, allyl, or acrylate moieties) present on oxo-metal clusters withthiol moieties (e.g., thiol moieties). Oxo-metal clusters include metaloxo (meth)acrylate clusters (“MOCs”), where “metal” refers to titanium,zirconium, zinc, and the like. “Metal oxo” and “oxo metal” are usedinterchangeably herein, and “metal oxo (meth)acrylate clusters” includemetal oxo acrylate clusters, metal oxo methacrylate clusters, and anycombination thereof. Curing a polymerizable composition with MOCsincludes crosslinking MOCs and thiol monomers. Suitable MOCs, such asZr₆(OH)₄O₄(O₂C(CH₃)═CH₂)₁₂, Zr₄O₂(O₂C(CH₃)═CH₂)₁₂,Zr₆(OH)₄O₄(O₂CH═CH₂)₁₂, Zr₄O₂(O₂CH═CH₂)₁₂, and the like, function as enemonomers.

Polymer composites formed with MOCs may include one or more of therepeating units shown in FIGS. 2A-2C, in which “Oxo-M-Cluster” may beone or more of Zr₆(OH)₄O₄(O₂C(CH₃)═CH₂)₁₂, Zr₄O₂(O₂C(CH₃)═CH₂)₁₂,Zr₆(OH)₄O₄(O₂CH═CH₂)₁₂, Zr₄O₂(O₂CH═CH₂)₁₂, the corresponding units withother metals, or the like, and n is an integer. The MOCs provide enefunctionalities to form polymers through crosslinking with thiolmonomers. Unlike polymer composites in which inorganic components areincluded as dopants, these polymer composites are formed with a majorityof the ene reactant in the form of MOCs.

MOCs may provide 1-100 wt % of the ene monomer in the composite mixture(e.g., 5-100 wt %, 10-100 wt %, 15-100 wt %, 20-100 wt %, 25-100 wt %,50-100 wt %, 75-100 wt %, or 90-100 wt %). In certain cases, MOCsprovide a majority of ene monomer in the composite mixture. The enemonomer may consist essentially of MOCs. That is, the MOCs may provideall or substantially all the ene functionality in the composite mixture.

The polymerizable composition may be partially polymerized before it isdisposed on the first substrate. Partial polymerization (e.g., in rangeof 30% to 50%) may be achieved, for example, by heating, irradiationwith UV light, or both, to an extent such that the partially polymerizedpolymerizable composition is in liquid form and thus can be poured ontothe first substrate. In one example, the polymerizable composition isheated in a range of 100° C. to 125° C. for 5-15 minutes after mixingand before the polymerizable composition is disposed on the firstsurface of the first substrate.

Referring again to FIG. 1, in 104, the polymerizable composition iscontacted with a first surface of a second substrate. The secondsubstrate may be at ambient temperature or may be heated before or whilethe polymerizable composition is contacted with the first surface of thesecond substrate. In one example, the second substrate is heated to atemperature that exceeds the temperature of the first substrate by 25°C. to 50° C. at the time the polymerizable composition is disposed onthe first surface of the first substrate. The second substrate istypically a disc or wafer with a thickness in a range from 300 μm to 10mm and a diameter in a range of 5 cm to 30 cm. The second substrate maybe made of a material such as quartz, glass, or silica. The TTV of thesecond substrate is typically in a range from 100 nm to 20 μm. Opticalperformance of the resulting photonic device is typically enhanced byincreasing thickness and decreasing TTV of the second substrate. In oneexample, the first surface of the second substrate is a flat surface. Inanother example, the first surface of the second substrate is apatterned surface, and the second substrate is a patterned mold, asdescribed herein with respect to the first substrate. Typically, atleast one of the first substrate and the second substrate is a patternedmold.

Before the polymerizable composition is contacted with the first surfaceof the second substrate, the second substrate may be coated with arelease layer. A thickness of the release layer is typically in a rangeof 1 nm to 30 nm thick. A release layer may be a fluorosilane coating, ametal coating, a metal oxide coating, or any other coating suitable foruse with a thiol-ene based polymer resin. In one example, a PDMS releaselayer is formed on the second substrate by a process that includescleaning the second substrate, coating the second substrate with a thinlayer of PDMS, and curing the PDMS by placing the second substrate on ahot plate and heating the substrate (e.g., at 200° C. for 15 min).

The polymerizable composition may be contacted with the first surface ofthe second substrate in such a way as to minimize defect formation dueto trapping of gas between the first substrate and the second substrate.In one example, contacting the polymerizable composition with thesubstrate includes forming an acute angle between the first substrateand the second substrate, and reducing the value of the acute angleuntil the first substrate and the second substrate are parallel andseparated by a predefined distance selected to yield a photonic devicewith a thickness in a range of 10 μm to 1 cm. Separation by thepredefined distance may be achieved by a spacer positioned between thefirst surface of the first substrate and the first surface of the secondsubstrate. In one example, two or more spacers are coupled to the firstsurface of the first substrate, the first surface of the secondsubstrate, or both.

In 106, the polymerizable composition is cured to yield a polymericstructure having a first surface in contact with the first surface ofthe first substrate, a second surface opposite the first surface of thepolymeric structure and in contact with the first surface of the secondsubstrate. Curing of the polymerizable composition, for example byheating only, by irradiating with UV radiation only, or by a combinationof heating and irradiating with UV radiation, may be selected to tunethe mechanical and optical properties of the resulting photonic device.In some cases, partial curing by UV irradiation is followed by heating(e.g., at a temperature in a range of 100° C. to 350° for 5 minutes to24 hours) to completely cure the polymerizable composition, therebyyielding a polymeric structure between the first surface of the firstsubstrate and the first surface of the second substrate.

In some embodiments, curing the polymerizable composition is achieved byirradiating the polymerizable composition with controllable, highintensity, uniform UV irradiation. As used herein, uniform UVirradiation generally refers to UV irradiation having an intensity thatis substantially constant throughout the duration of the irradiating ofthe polymerizable composition. As used herein, “substantially constant”UV irradiation intensity typically refers to a variation of UV intensitythroughout the duration of the irradiating of less than 20% of peakintensity. The use of UV radiation including UVA, UVB, UVC, or acombination thereof, from a uniform, large area, and collimated source,and having a power density of at least 10 mW/cm² promotes polymerizationand curing of a high index polymer substrate efficiently without leavingregions where the polymer chains are cured differently than others. Thepower density is typically less than 20,000 mW/cm². Differences incuring can include a different arrangement of polymer chains,non-uniformity in arrangement of polymer chains, and the like. When theUV intensity is not uniform and well-collimated, or scattering occurs,such as back scattering or scattering from surfaces proximate thepolymerizable composition to be cured, the polymer can undergodistortions at the bulk level, increasing TTV, reducing the overalltransparency of the resulting polymer, or both. A high intensity,uniform UV source may also uniformly heat the polymer to a temperatureless than 100° C., which can also aid in further curing of the polymerand improve its chemical stability.

This UV in-situ polymerization and curing process yields low TTV and lowbow/warp for polymeric structures having a thickness from about 200 μmto about 500 These polymeric structures can be fabricated as astandalone (free-standing) substrates or with a waveguide relief patternformed on at least one surface. Moreover, in some instances,polymerization in the absence of thermal curing can be achieved in lessthan 5 minutes and is thus suitable for rapid, cost-effective,large-scale production.

In 108, the polymeric structure is separated from the first substrateand the second substrate to yield a monolithic photonic device. Thepolymeric structure is typically allowed to cool to room temperaturebefore it is separated from the first substrate and the secondsubstrate. Separating the polymeric structure from the first substrateand the second substrate may include de-molding or peeling the polymericstructure off the first or second substrate. The monolithic photonicdevice is optically transparent and has a refractive index in the rangeof 1.6 to 1.9 or 1.7 to 1.9. In one example, the field of view (4:3aspect ratio) of the photonic device is up to 50°. The photonic devicehas a residual layer thickness in the range of 10 μm to 1 cm. As usedherein, “residual layer thickness” refers to the minimum distancebetween the first surface of the photonic device and the second surfaceof the photonic device.

In some cases, one or more of the operations in process 100 is replacedor combined with another operation, the order of one or more theoperations is interchanged, two or more operations occur simultaneouslyor continuously, or any combination thereof. In certain cases, process100 may include one or more additional operations as described herein.

FIG. 3 is a flowchart describing a second exemplary process 300 forfabrication of a monolithic, optically transparent, high refractiveindex photonic device from a curable high index polymerizablecomposition. Details regarding the substrates, the polymerizablecomposition, and the fabrication process described with respect toprocess 100 also apply to process 300 unless described otherwise.

In 302, a polymerizable composition is disposed between a first surfaceof a first substrate and a first surface of a second substrate. Thefirst surface of the first substrate and the first surface of the secondare separated (e.g., by spacers) to achieve a desired thickness of thephotonic device. Disposing the polymerizable composition between thefirst substrate and the second substrate may include injecting thepolymerizable composition between the two substrates. The firstsubstrate, the second substrate, or both may be heated (e.g., to atemperature in a range of 100° C. to 250° C.) while the polymerizablecomposition is disposed between the first substrate and the secondsubstrate.

In 304, the polymerizable composition is cured to yield a polymericstructure having a first surface in contact with the first surface ofthe first substrate, a second surface opposite the first surface of thepolymeric structure and in contact with the first surface of the secondsubstrate. Curing may be achieved by heating only, UV irradiation only,or a combination of heating and UV irradiation, such as described withrespect to FIG. 1. In 306, the polymeric structure is separated from thefirst substrate and the second substrate to yield a monolithic photonicdevice.

In some cases, one or more of the operations in process 300 is replacedor combined with another operation, the order of one or more theoperations is interchanged, two or more operations occur simultaneouslyor continuously, or any combination thereof. In certain cases, process300 may include one or more additional operations as described herein.

FIG. 4 depicts process 400 for fabricating an exemplary photonic device.Details of process 400 may be understood with respect to process 100unless described otherwise. First substrate 402 is a patterned moldhaving a first surface 404 with pattern 406 of protrusions andrecessions, as well as in-coupling grating 408. First substrate 402 iscoated with release layer 410. Second substrate 412 has first surface414 coated with release layer 416. First substrate 402 and secondsubstrate 412 are both heated before polymerizable composition 418 isdisposed on first surface 404 of the first substrate. Polymerizablecomposition 418 is a curable high index polymerizable composition asdescribed herein. Second substrate 412 is advanced toward the firstsubstrate 402 until the second substrate contacts spacers 420, therebyspreading polymerizable composition 418 between the first substrate andthe second substrate, filling pattern 406. Polymerizable composition 418is cured via UV irradiation only, heating only, or a combination of UVirradiation and heating, such as described with respect to FIG. 1, toyield polymeric structure 422. Polymeric structure 422 is cooled to roomtemperature and then separated from first substrate 402 and secondsubstrate 412 to yield monolithic photonic device 424. First surface 426of monolithic photonic device 424 has pattern 428 of protrusions andrecessions, as well as in-coupling grating 430. Monolithic photonicdevice 424 is optically transparent and has a refractive index in therange of 1.6 to 1.9. The field of view (4:3) of monolithic photonicdevice 426 is up to 50°.

In process 400, polymerizable composition 418 may be contacted with thefirst surface 414 of the second substrate 412 in such a way as tominimize defect formation in the resulting photonic device due totrapping of gas between the first substrate 402 and the secondsubstrate. In one example, as depicted in FIG. 5A, contacting thepolymerizable composition 418 with the second substrate 412 includesforming an acute angle α between the first substrate 402 and the secondsubstrate. Second substrate 412 is rotated toward first substrate 402 asindicated by the arrow, reducing the value of the acute angle α asdepicted in FIG. 5B. As depicted in FIG. 5C, rotation of secondsubstrate 412 continues until the first substrate 402 and the secondsubstrate 412 are parallel and separated by spacers 420, which define adistance selected to yield a photonic device with a maximum thickness ina range of 10 μm to 1 cm.

In another example, as depicted in FIG. 6A, second substrate 412 isflexed before contacting polymerizable composition 418, and the convexfirst surface of the second substrate is contacted with thepolymerizable composition. After contacting polymerizable composition418, the ends of second substrate 412 are advanced toward firstsubstrate 402 as depicted in FIG. 6B, reducing the value of angle α. Asdepicted in FIG. 6C, first substrate 402 and second substrate 412 areparallel and separated by spacers 420.

In yet another example, as depicted in FIG. 7A, first substrate 402 andsecond substrate 412 are flexed when the second substrate contactspolymerizable composition 418, and the polymerizable composition on theconvex first surface of the first substrate is contacted with the convexfirst surface of the second substrate. After contacting polymerizablecomposition 418, the ends of second substrate 412 are advanced towardfirst substrate 402 as depicted in FIG. 7B, reducing the value of angleα. As depicted in FIG. 7C, first substrate 402 and second substrate 412are parallel and separated by spacers 420.

Removing gas trapped between the first and second substrates may also beachieved by disposing the polymerizable composition on the firstsubstrate in a helium environment or by reducing, below atmosphericpressure, a pressure of the environment in which the imprinting processis performed before polymerization of the polymerizable composition isinitiated. Replacing trapped air with helium typically reduces defectsin the resulting polymeric structure, since helium escapes more readilyfrom solution than air. Reducing the pressure of the environment mayforce trapped gas toward edges of the first and second substrates. Aftertrapped gas is removed from the polymerizable composition, gascontaining oxygen (e.g., air) may be introduced as needed for curing ofthe polymerizable composition.

FIG. 8A depicts exemplary monolithic, optically transparent photonicdevice 800 having patterned first surface 802 and flat second surface804. Patterned first surface 802 has protrusions 806 and recessions 808.Protrusions 806 and recessions 808 may be uniform or vary in dimensions.Protrusions 806 are nanostructures, microstructures, or a combinationthereof, as described herein. Photonic device 800 has a residual layerthickness r in the range of 10 μm to 1 cm. As used herein, “residuallayer thickness” refers to the minimum distance between the firstsurface of the photonic device and the second surface of the photonicdevice.

FIG. 8B depicts exemplary monolithic, optically transparent photonicdevice 810 having patterned first surface 812 and patterned secondsurface 814. Patterned first surface 812 and patterned second surface814 have protrusions 806 and recessions 808. Protrusions 806 andrecessions 808 may be uniform or vary in dimensions. Protrusions 806 arenanostructures, microstructures, or a combination thereof, as describedherein. Photonic device 810 has a residual layer thickness r in therange of 10 μm to 1 cm.

For high volume or high quantity casting of polymeric structures, use ofinterchangeable UV transmissive casting plates or wafers designed toachieve appropriate spacing may include grooves or raised surfaces,thereby obviating the need for separate spacers. Such casting plates orwafers may be fabricated from fused silica or high quality quartz thathave high UV transmission at wavelengths greater than 200 nm. Having aspacer thickness integrated (e.g., machined, wet/dry etched, etc.) intothe casting plates helps ensure that a suitable gap distance ismaintained between stacked polymeric structures with application of asuitable force pushing the two plates together, where the gap distanceis maintained by the integrated spacer, and the gap is not susceptibleto variations due to casting tool vibrations during the operation ofproduction tools. Casting tool vibrations or other irregularities duringcasting can create undesirable TTV variations leading to poor imagequality.

FIGS. 9A-9D depict exemplary casting plates suitable for interchangeableinserts in production tools with pre-machined grooves for casting blankor patterned polymeric structures or films of a selected thickness. Eachfeature depicted in FIGS. 9A-9D has a TTV of less than ±1 μm. FIG. 9A isa perspective view of cylindrical casing plate 900. In one example,cylindrical casting plate 900 has a radius of 75 mm and a thickness of10 mm. FIG. 9B is a perspective and cross-sectional view of cylindricalcasting plate 910 having ledge 912 around its perimeter. In one example,a radius of cylindrical casting plate 910 is 75 mm, and a length ofledge 912 along the radius of the cylindrical casting plate is 15 mm. Athickness of cylindrical casting plate 910 is 10 mm at the center of thecasting plate, and a thickness of the ledge is 200 μm-500 μm (e.g., 350μm). FIG. 9C is a perspective and cross-sectional view of cylindricalcasting plate 920 having ledges 922 around portions of its perimeter. Inone example, a radius of cylindrical casting plate 920 is 75 mm, and alength of ledge 922 along the radius of the cylindrical casting plate is15 mm. A thickness of cylindrical casting plate 920 is 10 mm at thecenter of the casting plate, and a thickness of each ledge is 200 μm-500μm (e.g., 350 μm). FIG. 9D is a perspective and cross-sectional view ofrectangular casting plate 930 having spacers 932 in its corners. In someinstances, rectangular casting plate 930 is square. In one example,rectangular casting plate 930 is a square having a side length of 150 mmand a thickness of 10 mm. In one example, spacers 932 are square havinga side length of 15 mm and a thickness of 300 μm-500 μm (e.g., 350 μm).

Examples

A polymerizable composition was prepared by mixing tetravinylsilane and1,3-benzenedithiol in 1:2 molar ratio, respectively. To this monomermixture, 1% (w/w) photoinitiator (2-hydroxy-2-methylpropiophenone) wasadded to generate free radicals during UV exposure. A thiol-ene “click”composition was used within 1 min post mixing. The composition wasevenly dispensed at the center of the patterned quartz 550 μm plate andthe around 2″ in diameter. The top 1 mm plate was then brought incontact with 300 μm spacers kept between the two plates at the edges.The two plates and the uncured material in between were cured with anon-uniform UVA source. The UVA source had a 2″ diameter high intensityzone (˜110 mW/cm²) which was extended to fully cure up to a 5″ areausing a 5″ diffuser, which reduced intensity towards the edges to about˜30 mW/cm² or lower. FIG. 10A is an image of the resulting fullypatterned UV cured film (diameter of 5″) 1000, in which center portion1002 self-delaminated after curing. The intensity of the UV sourceduring curing of film 1000 is depicted in FIG. 10B, in whichpolymerizable composition 1004 is shown between casting plates 1006. UVintensity 1008 over the diameter of the casting plates 1004 results inself delamination of a center portion 1002 of polymeric film 1000.

FIG. 11 is a graph showing an average transmittance of light atwavelengths from 380 nm to 800 nm through a polymeric substrate.Transmission was measured using a spectrometer and a white light sourcehaving a 0° angle of incidence of the light source with respect to thesurface of the fabricated polymer substrate. The measured spot size wasabout 3 mm to about 5 mm in diameter. Multiple points were measured.

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made without departing fromthe spirit and scope of the inventions.

1. (canceled)
 2. A photonic device comprising: a monolithic structurecomprising a patterned surface defining protrusions and recessions,wherein the monolithic structure is composed of a cured polymericmaterial, a refractive index of the monolithic structure is at least1.6, and a minimum thickness of the monolithic structure is in a rangeof 10 μm to 1 cm.
 3. The photonic device of claim 2, wherein a dimensionof each protrusion and recession is less than 10 nm, less than 100 nm,less than 1 μm, less than 10 μm, less than 100 μm, or less than 1 mm. 4.The photonic device of claim 2, wherein the cured polymeric materialcomprises a thiol-ene based polymer.
 5. The photonic device of claim 4,wherein the cured polymeric material comprises a metal oxide.
 6. Thephotonic device of claim 5, wherein the cured polymeric materialcomprises 0.1 wt % to 30 wt % of the metal oxide.
 7. The photonic deviceof claim 6, wherein the metal oxide comprises titanium dioxide,zirconium dioxide, zinc oxide, or a combination thereof.
 8. The photonicdevice of claim 2, wherein the refractive index of the monolithicphotonic device is in a range of 1.7-1.9.
 9. The photonic device ofclaim 8, wherein the refractive index of the monolithic photonic deviceis in a range of 1.6-1.9.
 10. The photonic device of claim 2, whereinthe refractive index of the monolithic photonic device is at least 1.65.11. The photonic device of claim 10, wherein the refractive index of themonolithic photonic device is at least 1.7.
 12. The photonic device ofclaim 2, wherein the field of view of the photonic device (4:3 aspectratio) is up to 50°.
 13. The photonic device of claim 2, wherein thephotonic device is optically transparent.
 14. The photonic device ofclaim 2, wherein the photonic device is a lens.
 15. The photonic deviceof claim 2, wherein a transmittance of the monolithic structure isgreater than 80% between 400 nm and 800 nm.
 16. The photonic device ofclaim 2, wherein the patterned surface is a first patterned surface, andthe monolithic structure further comprises a second patterned surfaceopposite the first patterned surface.